How do I get the knee to bend the other direction?
EDIT: After inspecting the file you provided, the issue is that the leg bones actually bend backwards at the knee very slightly. In this case, Blender will never make the point point the direction you want. If you pull the knee joint forward a bit, or even just make the leg bones perfectly in line the IK will work as expected.

In the IK constraint options, right by where you selected the pole target, there is a Pole Angle option that will change the angle of the bend in relation to the target. Since yours is simply backwards, setting it to 180 degrees should do the trick.